Artificial line



Sept. 1, 1925;

' O. E. BUCKLEY ARTIFICIAL LINE Filed AUE. 5. 1922 \LlllllllllllllII/IILJ mmmom. l

. 4m l/lIsI/uzce 1mm Jim End f/Vaali r) Oil - Patented Sept. 1, 1925.

UNITED STATES PATENT oFF cE.

OLIV'EB IE. BUCKLEY, or uArLEwoon, new ma am, ASSIGNOB 'ro WESTERN ELEC-TRIO COMPANY, INCORPORATED, OF N YORK.

EW YORK, 11. Y., A CORPORATION or nnw ARTIFICIAL LINE.

Application filed August a, 1922. Serial in. 578,856.

To all whom it may concern: I

Be it known that I, OLIVER E. Buckner, a citizen of the United States ofAmerica residing at Maplewood, in the county it Essex and State of NewJerse have invented certain new and usefu Improvements in ArtificialLines, of which the following is a full, clear, concise, and exactdescription.

The principal object of the invention is to provide an artificial linethat shall accu-' simulate a long signaling conductor.-

ratel In t is specification there is disclosed as an example of theinvention, a balancing network for the duplex operation of a longhigh-speed continuously loaded ocean telegraph cable.

Fig. l is a diagram showing the particular-artificial line heredisclosed as representing the invention. Fig. 2 is a diagram showing thecurrent in the conductor at various distances from the sending end.

Fig. 3 is a permeability diagram for the loading material. Fig. 4 is adiagram showing the efi'e'ct of variation of air gap on effectivepermeabilit and Flg. 5 ma diagram showing the e ect on p ermeability ofsuperposed constant magnetizing force. I

In the United States patent application,

Serial No. 492,725, filed August 16, 1921,

(corresponding to British- Patent No. 184,774) in the name of O. E.Buckley, there is disclosed a continuously loaded conductor suitable foruse as a long ocean tele- In the specification of that case it ispointed out that the loading of long ocean telegraph cables hasheretofore been found of no practical advantage. In

deed, no telegraph cable of length greater than 100 nauts has beenloaded for any purpose, and the only loading of shorter cables has beenprimarily for tele hone use and in some cases secondarily or superposedtelegraphy.

A telephone cable of length 100 nauts has been loaded with a wrapping ofsmalliron wire, but the cable conductor described in the Buckley'patentapplication is loaded with tape of a special composition calledpermalloy which is fully described in the specification of thatapplication. I

A suitable form of permalloy is obtained by fusing together iron andnickel in the respective proportion of 21 per centand "7 8 per cent andformin the composition into a tape of suitable imensions. permalloy tapeis applied helically to the conductor, with the edges abutting.Thereafter, the taped conductor is given a heat treatment described inthe specification'reterred to, which leaves the permalloy tape in acondition of very high permeability for low magnetizing forces, manytimes higher than for the best samples of iron heretofore in'use. Y I IThe high permeability of the loading material gives the loaded conductora high inductance, thus diminishing the attenuation, and facilitates thetransmission of signals at much higher frequency than has been possible-on the unloaded cable conductors heretofore in use. p x

In the operation of long ocean'cables it has been quite usual heretoforeto operate them duplex. For this purpose, as is well known, artificiallines are provided "at both ends, each of which simulates the cableelec- ,trically to a practicable degree, .and the actual cable and theartificial line are connected up as arms of a Wheatstone bridge. Thematter 'of making and adjusting an artificial line so that it willsimulate a long ocean cable with suflicient accuracy has been one ofconsiderable difficulty, even though the cable was not loaded. "In'theUnited States patent application referred to, the continuously loadedline, is disclosed as be-' ing operated only one way. In the'particularexample there considered, the one Way operation was shown to be at aboutten times the speed for-the unloaded cable The unloaded cable has itsmessage capacityfinwith which comparison was proper;

This

loaded cable opan five times the difiiculty that maybe noticed. Thenonloaded cable has resistance and capacity,

whereas its'leakance and inductance are al-' most negligible. The'loadedcable "has a large amount of inductance "which, of course,

must be simulated in the artificial line, thus increasing the difiicultyof effecting a balance. Moreover, the inductance varies with respect tothe current, whereas the factors met inbalancing the unloaded cable,namely, resistance and capacity, are substantially the same fordifferent currents. Still further, the effective resistance of the lineis determined, in a measure, by eddy current losses and other effects int e loading materialso that this effective resistance for the loadedcable varies with chan e of the current, whereas for the non-loa edcable the efiective resistance is substantially constant.

With the conditions in view for simulating the lon continuously loadedconductor, I have evised an artificial line that is like the cableconductor with respect to all the essential constants involved, and maybe used to balance such a conductor for duplex operation, and may beadjusted in a convenientmanner to secure the desired balance.

The fparticular loaded cable considered by way 0 example in the Buckleypatent application has a cylindrical copper conductor of diameter 0.168inch. This is enveloped by a helically wound tape of permalloy ofthickness 0.006 inch and width 0.125 inch, which makes the overalldiameter of the taped conductor 0.180 inch. When applied in this way,the permalloy tape shows a virtual permeabilit of 2,000 or more, whereasfor any grade 0 iron heretofore available the figure would not be over200. By virtue of this extraordinary property of permalloy, its hi hpermeability at low magnetizing forces, t e conductor loaded in this wayserves for the high speed telegraph transmission described in theBuckley United States patent specification already identified.

After assembly of the cop r conductor and its loading material, asescribed, they are put through a heat treatment which de velops the highI 'rmeability referred to. Then the cover 0 gutta percha insulation,wires; etc.,is applied. The cable described by way of example has alength of 2,000 nauts. The magnetic properties of the loading materialwill a pear more fully in connection with the fo owing description ofthe artificial line.

Referring to Fi 1, the cable already described is indicate at 10. Thereceiver R is in the cross member of the 'Wheatstone bridge, twoadjacent arms of which on one side have the respective interposed equalcondensers C. The transmitter T is connected to the apex formed by thejunction of the conductors for these two condensers C. The remainintwo'ar'ms of the bridge are formed by the ca 'le 10 and the artificialline now to be described in detail.-

For the tgart of the artificial line lying nearest to e bridge, in anelectrical sense,

there is employed a series of conductors 11 of the same dimensions andmaterial as the cable conductors, and loaded in the same.

way. The cable conductors are surrounded with gutta ercha or. othersuitable insulation, but it 1s not necessa to simulate this condition inthe artificial line. The sections of ta d conductor in the artificialline may be 0 different lengths, shorter near the bridge and longer awayfrom it. However, more conveniently, they may be of the same length, sayeach feet. These sections will be connected in series throu h smalladjustable inductance coils 12 an resistances 13.

Condensers 14 are connected on one side to points adjacent to coils 12and on the other the inductive effects negligible between differentparts thereof.

There are four fundamental physical constants in the cable which mustfirst be considered for the pur ose of matching the artificial line tothe ca 1e, These are the resistance, capacity, inductance and leakance.Bfy making the conductor of the sections 11 o the same material andcross-section as the conductor of the cable, the series resistance perunit length is matched to a close first approximation. It is well knownthat cables are manufactured in sections which are spliced togetherbefore laying. The manufacturing methods employed necessarily result insmall differences for the constants for these sections. Whatever theconstants are for the various sections of the cable, it is assumed thatthey will be made the same for the corresponding sections of theartificial line 11, so that each naut of its 100 nauts will have thesame resistance as the corres 0nding naut of the cable. Precision of ajustment will be secured by the use of the small interposed adjustableresistances 13.

The portion 11 of the artificial line, has not only the same conductoras the cable, but it has the same inductive material wound helicallythereon. Therefore to a close first approxlmation the series inductanceof the artificial line 11 will be the same as of the first 100 nauts ofthe cable, naut for naut, but the small interposed adjustable inductancecoils 12 will facilitate making a recise adjustment to secure equalityof in notance between the cable and the artificial line, naut by naut.

The distributed shunt ca acity for the cable will be sufiicicntly simuated in the artificial line by the condensers 14, each with sending oneplate grounded'and the other plate connected to the cable at a. sixtyfoot interval.

Each condenser 14 will have substantially the same electrostaticcapacity as a sixty foot kw of the actual cab the effect of thedielectric hysteresis of the cable insulating material be closely sim-iulated.

The attenuation will determine a current in the actual cable that willbe somewhat as shown in-Fig. 2, where the abscissae represent distancesin nauts from the sending end and the ordinates represent the currentsat the corresponding ints in the cable.- At 100 nauts distance e currentwill have dropped from its sending value 0A to the value indicated bythe ordinate DP. Supposing that the whole arriving current at this pointwere reflected back toward the end, the current that would get back tothe sen end would be only that corresponding to e ordinate D'P'. But, ofcourse, any reflection irregularity will roduce only a small .fractionof a total refiection. It will be apparent that for irregularities inthe line further out, that is, say, further than 100 nauts along thecable, the effects due to partial reflections will be comparativelysmall at the sending end. Thus, it becomes apparent that it is the headend of the artificial line for which the most accurate adjustment isrequired, and that is the reason why the continuously loaded artificialline 11 has been employed for the head end as shown in Fig. 1 instead ofan artificial line with lumped loadin After this continuously loadedartificial e has been carriedto a suitable length, as at the point- 17in Fig. 1, it is continued in the form of an artificial line made up oflumped elements as will now be explained. I

For the part of the artificial line correspond' to the next few hundrednauts of the cab e, there are provided sets of elements in succession,each set comprising a series inductance coil 19, a series resistance 18and a shunt condenser 20. To a first approximation, the inductance coil.19 has an inductance slightly lem than a certain definite length of thecable 10; the resistance 18 (with w atever resistance may be in the coil19) is the same as the resistance of the same length ofthe cable 10, andthe condenser 20 has the same capacity as the capacity of that samelength of the cable 10.

Associated with each such group of coils Hand 18 and condenser there arealso a small adjustable air core inductance coil The 21 in'series and anadjustable hi h resistance coil 30 in shunt to the con euser 20. Thefunction of the resistance 30 is substantially the same as of theresistance 16. The con enser 20 is more nearly perfect than thedistributed capacity of the cable, and

the resistance 30 in shunt to the condenser 20 makes the functionallikeness more nearly exact. ductance coil 21 will be explainedpresently.

The magnitudes of the successive resistances 18 and coils 19 may begraded, being made smaller at locations closer to the bridge and thusfacilitating closer adjustmentwherethesimulation to the actual lineneeds'to be more exact. In this case the condensers 20 will be graded inlike manner.

The use of the inductive material on the cable causes it to have aninductance L that is not constant but is dependent on the magnitude ofthe current. This may be pointed out with reference to Fig. 3. The curve22 is the ordinary B-H curve for permalloy, with ap ropriate'scales forthe co-ordinates. H stan s for applied magnetizing force and B standsfor the magnetic induction developed in the material. The curve 23 inthe same figure is the p.H curve where pzB/H. The values of H involvedin cable transmission are low and they fall off vary rapidly withdistance from-the transmitting end, so that beyond the first hundrednauts of the cable and in the corresponding part of the artificial lineonly a narrow range, say from O to X on ig. 3 is involved.

By the application of suitable constant factors of proportionality,the'p.H curve can also be regarded as an LI curve, where L is theinductance and I is the current. roblem of simulating the loaded linemay c said to involve the problem of making the artificial line have thesame Ll curve as the cable. This means that for corresponding points inthe two lines, the LI curve shall be the same for both lines. Inaddition the hysteresis loss in the artificial line must be the same ateach point as for the corresponding point along the length of the cable,but at points far out on the cable, its effect will be practicallynegligible, and the criterion of matching the LI curves will besufiicient. If the inductance were constant the LI curve would be ahorizontal line but its slope expresses the fact that the inductance isa ratio whose value varies dependently upon the. variation of thecurrent. If the core material is different from permalloy then it mustbe worked at a flux density to compensate for the difierence and makethe LI curve the same for the ermalloy loaded cable and the artificialine. In. the present case, in order to make the lumped artificial lineas nearly as possible like the cable, the same inductive material isemployed, that is, the cores of the The purpose of the adjustableincoils 19 are made of permalloy, heat-treated and otherwise prepared inthe same way as the permalloy tape wound on the cable itself. By thisfeature of construction an imp-p111:- tant step is taken to make theartificial e closely simulate the actual line.

cores of the inductance coils 19,

Not only is permalloy employed for the ut in addi tion these coils andcores are designed so that the permalloy is worked at the same magneticdensity as in the cable, that is, if a steady current .of a certainnumber of microamperes flowin duces a certain flux ensity in thematerial ofthe surrounding tape, then the coils 19 are designed so thatthe same current flowing in their windings will produce the same fluxdensity in their core material. In this way, the assurance is gainedthat the same curve 23 in Fig. 3 will be followed for correspondingpoints of the cable and the artificial line.

In the cable certain losses due to eddy currents in the loading materialwill be inevitable and accordingly the cores of'the coils 19 arelaminated to such a thickness as to make the alternating current losseshere the same as in the cable for the same currents in the respectiveconductors.

Another feature of construction that is employed in connection with theseries inductance coils 19 is to make them with air gaps and to makethese air gaps adjustable. The purpose of the adjustable air gaps is toadjust the inductance of the coils. An increase of the air gap willdiminish the inductance of the coil, and vice versa. However, the sameincrease of the air gap that diminishes the inductance will more rapidlydiminish the rate of variation of the inductance with current strength.In other words, referring to Fig. 4, an increase of the air gap, willchange the LI curve from 27 to 28, but if the ordinates are multipliedbya constant-for curve 28, it cannot be brought to coincide with curve 27but may be brought to such a locus as curve 29. This is shown by thefollowing considerations.

Let

M=magnetomotive force impressed in the circuit,

Rzreluctance of circuit,

B=fiux density at the air gap, lzlength of the iron portion of thecircuit,

Z =length of the air gap,

Azcross-sectional area of the air gap,

H =magnetic field intensity in the iron,

The equations of a magnetic circuit comprising a number of 11'011elements of various along the cable prodimensions and permeabilities,and an air gap, are- M=BA-R (I) and- I h=2 (2) MA: A

Zl,=l

where g. may be considered as the mean permeabllity of the iron.Equation (1) becomes a and can be written in the two forms- H=HX+HRI andwhere a may be termed the effective permeability of the air gap, is theeffective permeability, and H= is the mean magnetic field intensityaround the circuit or the actual field intensity in the absence of anair gap. From equation (4) p. can be computed when the value of p. andthe dimensions of the air gap are known.

The variation of the effective permeability with impressed fieldintensity H will now be determined. For small values of H the p.H curvefor iron can be written- =no( therefore- B F( l) i =I o i l o l l o land- Fe whence- This relation can inverted by substitutwhereterms of a,b, p...

(4). Substituting (8) in (6) gives B in terms of H- whence Fromequations (10) and (11) it is evident that the introduction of an airgap in a magnetic circuit causes 'a' much greater reduction in rate ofchange of permeability than in the permeability itself. For example, ifthe air gap is such as to reduce where the initial effectivepermeability of the circuit to one half its previous value the rate ofchange of permeability is reduced to oneeighth its former value forsmall values of H, or the ratio of rate'of change ofpermeability toinitial permeability is reduced to one-fourth of its former value.

Having provided for adjustment of the air gap of each coil 19, theforegoing considerations show that this introduces an undesirable changein the ratio of rate of change of inductance to current strength. Withthe end in view to compensate this efiect, the small series adjustableair core inductances 21 are employed. By means of an adjustableinductance 21, the inductance can be varied Without varying the rate atwhich the inductance changes with current? so that with the twoadjustable'coils 19 an 21, a desired adjustment of both of these factorscan be secured.

Farther out on the artificial 'line a dif ferent method is employed foradjusting the inductance of the coils, as shown for the coils .19. Thesemay be made with rmalloy cores like the others, but they 0 not haveadjustable air gaps and the adjustable air core coils 21 are notemployed. v

and resistances designated 32 in and Around each core for the seriesartificial line windin s 19 there is a separate conductive win ing 24and in circuit therewith a battery and an adjustable resistance 25. Asshown in Fig. 5, it will be seen that although L varies with Iordinarily as shown by curve 27, yet for a superposed direct current anda narrow range of associated variable current, the apparent value of L'varies as shown by curve 26. By adjusting the direct current in thewinding by means of the adjustable resistance 25 the core is kept at anydesired point on the curve 26 of Fig. 5,and since the ordinates of thiscurve represent inductance it will be seen that an adjustment ofinductance is secured bythis-means. w

Still farther out on the. artificial: line, wherereflection;irregularitieswwi1l.- be e'xsaid sections and in seriestherewith.

' 3. An artificial line comprising continuously loaded conductorsections m series, lumped im dance elements between said sections an inseries therewith, and shunt lumped impedance elements connected betweensaid sections.

4. An artificial line comprising continuousl loaded conductor sectionsin series, and umped inductance elements between said sections.

5. An artificial line comprising conductor sections in series, each withuniform inductance in substantial amount, and small adjustable lumpedinductances alternating with said sections in series.

6. An artificial line comprising continuously loaded conductor sectionsin series and small adjustable lumped inductances and resistancesbetween consecutive section in series. I v

7. An artificial line comprising contin-- uously .loaded conductorsections in series, shunt condensers connected between consecutivesections, and high resistances in parallel with said condensers.

8. An artificial line comprising conductor sections continuously loadewith a magnetic alloy consisting chlefl of nickel and iron,

adjustable lum in uctancev elements between said sect ons and in seriestherewith,

umped impedance elements between I tinuously loaded with a magneticalloy consisting chiefly of nickel and Iron, and an artificial line forbalancing said cable comprising two sections of conductor of the samekind as the main cable core and loaded with said alloy in the samemanner, an adjustable lumped inductance between said tions, a pluralitof lumped inductance coils in said artificial line more remote from theconnection to said cable than said continuously loaded sections, and acore composed of said alloy for each of said coils.

10. In combination, a smooth signaling conductor, transmitting andreceiving apparat'us associated with one end thereof and a balancin thatend, t e part of said line nearest said end comprising series connectedsections of smooth conductor like said signaling conductor in respect tothe series impedance characteristics thereof and lumped shunt impedancedevices connected in alternation with said sections. corresponding invalue withrthe shunt impedance characteristics of the portions of thesignaling conductor of the same lengths as the corresponding sections.

11. In combination, a smooth signaling conductor, transmitting andreceiving apgaratus associated with one end thereof an a balancingartificial line connected with that end, the part of said line nearestsaid end comprising series connected sections of smooth conductorapproximately like said signaling conductor and small adjustable lumpedelements in series between the sections tofacilit-ate exact adjustment.

12. In combination, a smooth signaling conductor, transmitting andreceiving apparatus associated with one end thereof, and a balancingartificial line connected with that end, the part of said line nearestsaid end comprising series connected sections of smootliaconductor likesaid signaling conductor, condensers connected in shunt between thesections and having substantially the same capacity as lengths of thesignaling conductor corresponding to said sections, and adjustableresistances in parallel with said condensers to make the total shuntpath at each point between' sections of the same value and character asthe distributed shunt path for the corresponding part of the signalingconductor.

13. In combination in an artificial line, sections of continuouslyloaded conductor, small adjustable inductances and resistancesinterposed in series between such sections and adjustable condensers andresistances connected in shunt between said sections.

14. In combination, a signaling conductor loaded continuously by meansof a certain permeable material, transmitting and. re-

ceivmg apparatus associated with one end artificial line connected withthereof and a balancing artificial line concomprising coils with .thesame material sectlons, a shunt condenser between said secf or theircores. 4

,15. In an artificial line to simulate a con- I tinuously loaded'line,inductance coilshaving adjustable air gaps.

16. In an artificial line to simulate a continuously loaded line,inductance coils having adjustable air gaps and in series alternationtherewith adjustable air core inductance coils.

17. In an artificial line to simulate a continuously loaded signalingconductor, two

kinds of adjustable inductance coils in series alternation, one with acore of permeable material and an adjustable air gap, the other with anair core and adjustable as to its inductance, whereby, with relativeadjustment, the signaling conductor can be simulated.

18. In combination, a signaling conductor continuously loaded with'acertain permeable composition, transmitting and receiving apparatusassociated withone end thereof and a balancing artificial line connectedwith that end and comprising coils with cores of the same said materialand with adjustable air gaps, the dimensions of said coils and coresbeing such that the material isworkedat the same magnetic flux densityas on the signaling conductor.

19. In combination, a continuously loaded signaling conductor,transmitting and receiving apparatus associated with one end thereof anda balancing artificial line connected with that end, said artificialline com prising inductance; coils with cores, .said coils and' coresbeing proportioned togive the same inductance current characteristic inthe artificial line as in the signaling conductor.

20. In combination, a continuously loaded signaling conductor,transmitting and receiving apparatus associated with one end thereof anda balancing artificial line connected with that end, said linecomprising coils and cores with adjustable air gaps for which theadjustment varies the inductance less than the rate of change ofinductance with current, and adjustable air core coils in series bywhich com nsation may be effected to make the artitib ial line simulatethe loaded conductor.

21. In combination, a signaling conductor continuously loaded with amagnetic alloy smooth conductor continuously loaded with said alloy likethe signaling conductor and the said line farther out comprising coilshaving cores composed of said alloy. v

22. In combination, a continuously loaded signaling conductor,transmitting and receiving apparatus associated with one end thereof anda balancing artificial line connected with that end, said linecomprising series elements and shunt condensers at intervals, each saidcondenser having an adustable high resistance in parallel therewith.

23. In an artificial line to simulate a continuously loaded signalingconductor, inductance coils in series and resistances connected inseries alternately with said coils,

the values of said resistances being enough,

when taken with the resistances of the inductance coils to simulate theline with respect to both inductance and resistance.

24. In combinatioma continuously loaded signaling conductor,transmitting and receiving apparatus associated with one end thereof anda balancing artificial line connected with that end, said linecomprising inductance coils with cores of permeable ma- -terial,auxiliary coils on said cores and adustable direct current sources toenergize said last mentioned coils.

25. In an artificial line to simulate a continuously loaded signalingconductor, in-

- ductance coils with cores of the same mate- 27. The'coinbination witha continuously loaded signaling conductor, of an artificial linesimulating said conductor including inductance coils with cores of thesame material as the loading material, said coils and cores beingdesigned to have an LI curve for each point of the artificial linesimulating that of the corresponding point of the signaling conductorand also simulating the hysteresis loss of the loaded signalingconductor.

' 28. The method of producing a balancing impedance in an artificialline equal to the impedance of a signaling conductor eontinuously loadedwith magnetic material, which consists in working the magnetic materialat each point of the artificial line on approximately the same LI curveas for the corresponding point of the signaling conductor.

29. The method of producing a balancing impedance in an artificial lineequal to the impedance of a signaling conductor continuously loaded withmagnetic alloy, which consists in working the magnetic material at eachpoint of the artificial line on a proximately the same LI curve as has te corresponding point'of the signaling conductor and at the samehysteresis loss.

'30. The method of adjusting the inductance of the coils in anartificial line to balance a continuously loaded signaling conductor,which consists in introducing a variable amount of substantiallyconstant permeability substance in the magnetic circuits of at least aportion of said coils.

31. The method of adjusting the inductance of coils in an artificialline to balance a continuousl loaded signaling conductor, which consistsin super-posing the field of a local direct current on the cores of saidcoils and adjusting the magnitude of said direct current.

In witness whereof, I hereunto subscribe my name this 2nd day of AugustA. D., 1922.

OLIVER E. BUCKLEY.

